Buggy code:
public class SummaryStatistics implements Serializable , StatisticalSummary { private static final long serialVersionUID = - 2021321786743555871L ; protected long n = 0 ; protected SecondMoment secondMoment = new SecondMoment ( ) ; protected Sum sum = new Sum ( ) ; protected SumOfSquares sumsq = new SumOfSquares ( ) ; protected Min min = new Min ( ) ; protected Max max = new Max ( ) ; protected SumOfLogs sumLog = new SumOfLogs ( ) ; protected GeometricMean geoMean = new GeometricMean ( sumLog ) ; protected Mean mean = new Mean ( ) ; protected Variance variance = new Variance ( ) ; private StorelessUnivariateStatistic sumImpl = sum ; private StorelessUnivariateStatistic sumsqImpl = sumsq ; private StorelessUnivariateStatistic minImpl = min ; private StorelessUnivariateStatistic maxImpl = max ; private StorelessUnivariateStatistic sumLogImpl = sumLog ; private StorelessUnivariateStatistic geoMeanImpl = geoMean ; private StorelessUnivariateStatistic meanImpl = mean ; private StorelessUnivariateStatistic varianceImpl = variance ; public SummaryStatistics ( ) { } public SummaryStatistics ( SummaryStatistics original ) { } public StatisticalSummary getSummary ( ) { } public void addValue ( double value ) { } public long getN ( ) { } public double getSum ( ) { } public double getSumsq ( ) { } public double getMean ( ) { } public double getStandardDeviation ( ) { } public double getVariance ( ) { } public double getMax ( ) { } public double getMin ( ) { } public double getGeometricMean ( ) { } public double getSumOfLogs ( ) { } public double getSecondMoment ( ) { } @ Override public String toString ( ) { <START_BUG> StringBuffer outBuffer = new StringBuffer ( ) ; <END_BUG> String endl = "\n" ; outBuffer . append ( "SummaryStatistics:" ) . append ( endl ) ; outBuffer . append ( "n:<seq2seq4repair_space>" ) . append ( getN ( ) ) . append ( endl ) ; outBuffer . append ( "min:<seq2seq4repair_space>" ) . append ( getMin ( ) ) . append ( endl ) ; outBuffer . append ( "max:<seq2seq4repair_space>" ) . append ( getMax ( ) ) . append ( endl ) ; outBuffer . append ( "mean:<seq2seq4repair_space>" ) . append ( getMean ( ) ) . append ( endl ) ; outBuffer . append ( "geometric<seq2seq4repair_space>mean:<seq2seq4repair_space>" ) . append ( getGeometricMean ( ) ) . append ( endl ) ; outBuffer . append ( "variance:<seq2seq4repair_space>" ) . append ( getVariance ( ) ) . append ( endl ) ; outBuffer . append ( "sum<seq2seq4repair_space>of<seq2seq4repair_space>squares:<seq2seq4repair_space>" ) . append ( getSumsq ( ) ) . append ( endl ) ; outBuffer . append ( "standard<seq2seq4repair_space>deviation:<seq2seq4repair_space>" ) . append ( getStandardDeviation ( ) ) . append ( endl ) ; outBuffer . append ( "sum<seq2seq4repair_space>of<seq2seq4repair_space>logs:<seq2seq4repair_space>" ) . append ( getSumOfLogs ( ) ) . append ( endl ) ; return outBuffer . toString ( ) ; } public void clear ( ) { } @ Override public boolean equals ( Object object ) { } @ Override public int hashCode ( ) { } public StorelessUnivariateStatistic getSumImpl ( ) { } public void setSumImpl ( StorelessUnivariateStatistic sumImpl ) { } public StorelessUnivariateStatistic getSumsqImpl ( ) { } public void setSumsqImpl ( StorelessUnivariateStatistic sumsqImpl ) { } public StorelessUnivariateStatistic getMinImpl ( ) { } public void setMinImpl ( StorelessUnivariateStatistic minImpl ) { } public StorelessUnivariateStatistic getMaxImpl ( ) { } public void setMaxImpl ( StorelessUnivariateStatistic maxImpl ) { } public StorelessUnivariateStatistic getSumLogImpl ( ) { } public void setSumLogImpl ( StorelessUnivariateStatistic sumLogImpl ) { } public StorelessUnivariateStatistic getGeoMeanImpl ( ) { } public void setGeoMeanImpl ( StorelessUnivariateStatistic geoMeanImpl ) { } public StorelessUnivariateStatistic getMeanImpl ( ) { } public void setMeanImpl ( StorelessUnivariateStatistic meanImpl ) { } public StorelessUnivariateStatistic getVarianceImpl ( ) { } public void setVarianceImpl ( StorelessUnivariateStatistic varianceImpl ) { } private void checkEmpty ( ) { } public SummaryStatistics copy ( ) { } public static void copy ( SummaryStatistics source , SummaryStatistics dest ) { } }

Fix:
StringBuilder outBuffer = new StringBuilder ( ) ;